The present invention is related to disc drive data storage systems and, more particularly, to a method of controlling curvature of a transducing head, such as a hydrodynamic bearing slider.
Disc drives of the xe2x80x9cWinchesterxe2x80x9d type are well known in the industry. Such drives use rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective head gimbal assemblies (HGAs). Head gimbal assemblies carry transducers which write information to and read information from the disc surface. An actuator mechanism moves the head gimbal assemblies from track to track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a load beam for each head gimbal assembly. The load beam provides a preload force which urges the head gimbal assembly toward the disc surface.
The head gimbal assembly includes a gimbal and a slider. The gimbal is positioned between the slider and the load beam to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc. The slider includes a slider body having a bearing surface, such as an air bearing surface, which faces the disc surface. As the disc rotates, the air pressure between the disc and the air bearing surface increases, which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. The preload force supplied by the load beam counteracts the hydrodynamic lifting force. The preload force and the hydrodynamic lifting force reach an equilibrium which determines the flying height of the slider. The transducer is typically mounted at or near the trailing edge of the slider.
In some applications, the slider flies in close proximity to the surface of the disc. This type of slider is known as a xe2x80x9cpseudo-contactxe2x80x9d slider, since the bearing surface of the slider can occasionally contact the surface roughness of the disc. In other applications, the slider is designed to remain in direct contact with the disc surface with substantially no air bearing. These sliders are referred to as xe2x80x9ccontact recordingxe2x80x9d sliders.
It is often desirable to fabricate a slider such that the bearing surface has a positive curvature along the length and width of the slider. Length curvature is known as crown curvature. Width curvature is known as cross or camber curvature. The proper setting and control of crown and cross curvature reduces flying height variability over varying conditions, improves wear on the slider and the disc surface, and improves takeoff performance by reducing stiction between the slider and the disc surface. In a typical slider fabrication process, crown or cross curvature is created by lapping the bearing surface on a spherically-shaped lapping surface or on a flat lapping surface while rocking the slider body back and forth in the direction of the desired curvature. The amount of curvature is determined by the radius of the rocking rotation. This lapping process is difficult to control and results in large manufacturing tolerances. U.S. Pat. Nos. 5,442,850; 5,266,769; 5,982,583 and 6,073,337 disclose various other methods for setting slider curvature by altering surface stresses in the slider body material during fabrication of the slider body. The curvature of the slider is then fixed after fabrication.
However, as technology evolves and recording density increases, sliders must fly closer to the magnetic surface of the disc to maintain signal strength. Lower fly heights will necessitate tighter tolerances on fly height to avoid head-disc interactions. Currently, as was mentioned above, target fly heights are achieved by precisely controlling the dimensions of the slider (which carries the recording head) during the manufacturing process. In the future, however, manufacturing limits will be reached, and effective methods for adjusting slider geometry after fabrication will be needed. For instance, adjustments could be made before the drive is qualified for service or actively while the slider is flying.
Instead of relying on optimized passive air bearing surfaces and fabricated crown curvatures to control slider fly heights, various approaches to actively controlling slider fly height during operation of a data storage system have been proposed both for recording heads and glide heads. Generally, with prior curvature control methods, each active change in crown curvature results in a corresponding change in cross curvature and vice versa. For example, the properties of piezoelectric deformable material used in active slider actuation typically require changes in crown and cross curvature to be coupled. Crown curvature change is due to expansion or contraction of the deformable material in a longitudinal direction, while cross curvature change is due to expansion or contraction of the deformable material in a transverse direction. The expansion/contraction of the deformable material in the two directions is typically coupled, which results in the coupling of changes in crown and cross curvature.
In many instances, the coupling of changes in crown and cross curvature proves to be disadvantageous because the effects of adjustment in each type of curvature may be opposite in nature, and each could be desirable in certain situations. For example, fly height is positively related to crown curvature and negatively related to cross curvature. In addition, slider fly height is more sensitive to changes in crown curvature than cross curvature, but if cross curvature becomes too high as a result of crown actuation, the roll stability of the slider may be compromised. Conversely, if cross curvature becomes too low (negative), the rails of the slider may contact the disc. Also, it should be considered that crown and cross curvature values for each particular slider can vary from one slider to the next and in different directions based on variances in prior fabrication processes. Therefore, it is desirable to de-couple the actuation of crown and cross curvature as much as possible to enable fly height change to be maximized. It is also desirable to enable actuation of one curvature type preferentially over the other.
An improved method and apparatus are desired for actively controlling slider fly height during operation of the disc drive.
One aspect of the present invention pertains to a slider for actively controlling a fly height of the slider relative to a data storage disc. The slider includes a slider body having an air bearing surface, a back surface opposite the air bearing surface, a length, a width, a longitudinal axis, a transversal axis, a crown curvature located on the air bearing surface along the length of the slider body and a cross curvature located on the air bearing surface along the width of the slider body. The slider also includes a first plurality of beams that are disassociated from one another, constructed of deformable material and affixed to the back surface of the slider body. Each beam within the first plurality of beams, in response to an applied electrical control signal, is deformable in a first dimension parallel to the back surface of the slider body.
Another aspect of the present invention pertains to a slider for actively controlling a fly height of the slider relative to a data storage disc. The slider includes a slider body having an air bearing surface, a back surface opposite the air bearing surface, a length, a width, a longitudinal axis, a transversal axis, a crown curvature located on the air bearing surface along the length of the slider body and a cross curvature located on the air bearing surface along the width of the slider body. The slider also includes a first layer of deformable anisotropic material affixed to the back surface of the slider body and having a length and width that respectively and substantially coincide with the length and width of the slider body.
Another aspect of the present invention pertains to an apparatus for actively controlling a slider. The apparatus includes a disc rotatable about a central axis and having a recording surface. The apparatus also includes disc head slider means for carrying a transducer at a fly height relative to the recording surface during rotation of the disc and for actively altering at least one of a crown and cross curvature of the disc head slider to a greater extent than the other of the crown and cross curvature to adjust the fly height during rotation of the disc.